Convenient way of depicting the thermodynamics of reactions. Typically, the y-axis is given in units of energy, and the x-axis is defined as the reaction coordinate (see left). The reaction coordinate is a very general entity which you can think of as the progress of the reaction. It is similar to time, but, the reaction coordinate has no units and no scale. We simply use it to show
different stages of the reaction. Usually, the reactants are drawn at a certain level on the left side of the reaction coordinate, and the products are given on the right. A curved line connects the reactants and the products and shows the energies of any intermediates and/or transition states present in the reaction.